Germany Mi# 179 - Colors Under UV

Since I am in Northern California (Sheltering in place), there was some time to sort stamps. I had a few bags of early BRD Theodor Heuss stamps and searched for Fluorescent variety (Mi# 179y - 186y).
To my surprise I found that #179 has 4 very distinct colors under UV. Sorry for the picture quality (took it with my cell phone), but visually color variations are even more obvious.
Fluorescent one (179y) is certainly on the right, but what about other 3 colors? Michel is not mentioning anything about them - there is only one other option - 179x.
I actually have dozens of stamps of each color, so it is not like couple of stamps got damaged by some chemical. Please let me know if you have any additional information . Thanks

Yes, I noticed the reaction UV light with my Mi 179x, 5 pf Heuss stamps a few years ago while checking for fluorescent paper.

They must have been using different ink formulations, but I haven't seen anything published about this.

I have the best examples mounted on my Heuss "used" page. I describe mine as 4 types: orange red, dark orange red, carmine, and violet.

A few days ago, I came across this page. It is in German, but we have Google Translate these days - if you do not know German -.

https://forum.bdph.de/showthread.ph...se-Beispiele